Thanks to the advanced technology and relatively matured semiconductor techniques, digital cameras using complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) as the image sensing elements thereof can now present high-quality images. Even the consumptive-grade cameras can satisfy the general consumers' demands for image color and high definition. Currently, the advanced digital single-lens reflex (DSLR) cameras have also been widely accepted among critical professional photographers to almost replace the role of the conventional cameras using film. Now, with the further reduced selling price thereof, the small-size digital cameras have become highly popular among general users, and there is incredible growth in the number of users of the professional-grade DSLR cameras, too. Taking photos is no longer an expensive leisure activity. Everyone can obtain rich information about cameras and photography over the Internet and learn to be a good photographer. Meanwhile, various kinds of special applications and requirements are developed in response to the prosperous growth of digital camera market.
However, as being limited by some bottlenecks in the currently available technology, the image sensing elements of the digital camera have relatively narrow latitude of environmental brightness. The image sensing elements using CMOS or CCD have latitude of brightness about 5 EV, which is apparently much lower than the 10 EV obtainable from the conventional film. When taking a picture in an environment with relatively high contrast in brightness, such as taking a sunset picture, and measuring the amount of light in the low-brightness area, the obtained picture would show overexposure around the setting sun. In the overexposure condition, the image has color scale that could not show color gradations to thereby lose details of the image. This condition is of course not acceptable by users who require for high image quality.
Currently, there are many ways to overcome the above-mentioned problem. For example, a user can use different exposure values to take several pictures of the same scene for showing different brightness levels, and then use advanced image processing software to do spectrum analysis and other adjustment and processing to synthesize several pictures, so as to show the details that are lost in the overexposed image. However, such image processing requires relatively complicated procedures and only persons who have rich experiences and sufficient technical background in the photographical field can well manipulate these techniques to obtain a perfect photograph.